Larger and higher rated (8 MW to 12MW) offshore wind turbines are being increasingly constructed in challenging environment. Examples include but are not limited to a combination of deeper waters, further offshore, soft soils together with gassy materials, typhoon/ hurricane zone, seismic hazard zones, liquefaction zones. One of the unique feature of wind turbine system is the proximity of the operating rotor frequency (1P) to the resonant frequency of the system which makes these structures dynamically sensitive. The aim of the lecture is to discuss the design challenges and possible ways to make progress on our understanding. Lessons learnt from small scale model tests will be highlighted and ways to upscale the results will be discussed. Methods for certification of new types of foundation will be discussed together with some examples.